Hello. For a street car that produces good vaccume at lower rpms and doesn't have enormous venturis is there a significant advantage to annular boosters over down leg etc.? Thanks, Jon

 

Yes there is.

Idle vacuum really doesn't matter, it's not connected with the issues at hand.

Annular boosters create a much larger "signal", i.e. more venturi vacuum (NOT the same as idle vacuum), to draw the fuel out of the bowl with. Consequently they're FAR easier to tune, and give better fuel control especially at light throttle and low RPMs. That's why the better Holleys have them, as opposed to the "budget" carbs like the 1850, and why people who know are willing to pay extra to get them.

 

That's what I was looking for. Thanks! Jon

 

..... but don't think you're going to just "upgrade" to them with an existing carb that currently has more common straight leg or down leg boosters. Annular discharge units produce a MUCH different vacuum signal and completely change the calibration of the carb's main circuits. Stuff you can't just change jets and make it work right.

You either buy a carb that's built with them from the get-go or you don't use them. Doing an "upgrade" to annular boosters in an existing carb is best left to the pros. Air bleeds, metering blocks, emulsion tubes, etc. will all need to be changed to work properly with them.

 

Thanks Damon, I wasn't expecting to be able to modify my existing carb to that extent. But it looks like I'll be shopping for a carb soon and I was wondering if annular boosters are worth the extra money. I don't actually see any carbs on Holley's site that are so equipped. I'm pretty sure that Year One sells carbs that have been reworked.."Hardcore Plus" I think they're called.